Polysaccharides such as cellulose are natural biological homopolymers of glucose residues linked in a 1,4-beta configuration. Such glucan chains associate with one another and form useful insoluble threads or strands.
Cellulose is an extremely abundant macromolecule. Estimates for its yearly production range between 10.sup.9 and 10.sup.11 tons. Because of its abundance and useful physical properties cellulose has been employed as the starting material for a wide variety of articles of manufacture ranging from absorbents, to materials of construction, to fillers for food products.
Cellulose and like polysaccharides are synthesized not only by various plant systems, such as grasses, trees, cotton plants, and the like, but also microorganisms. For commercial uses the plant systems, e.g., trees and cotton plants, are the primary sources of cellulose.
Isolation of cellulose from wood is performed usually by three commercial processes: the sulfite process, the sulfate process, and the soda process. The objective is to separate individual cellulose fibers with minimum mechanical damage as the wood is comminuted or pulped, and to then selectively recover these fibers while leaving behind the other constituents of the wood or other plant material source. Various pulping processes are known.
However, the cellulose recovered from a pulping process is relatively coarse. Also, the recovered fibers are relatively short in length and have relatively large effective diameter. For example, the recovered cellulose fibers are about 0.5 to about 4 millimeters in length, and have a width of about 0.02 to about 0.07 millimeters. However, for many applications fibers of such dimensions are much too coarse.
Cellulosic fibers that are several orders of magnitude finer are produced by microorganisms. While the existence of microbial cellulose has been known for about 100 years, it has remained by and large a laboratory curiosity.
An approach to reduce further the size of pulp is described in U.S. Pat. No. 4,374,702 to Turback, which patent describes a methods for the production of microfibrillated cellulose.
The structure of natural microbial cellulose membranes has been described by Purz et al. in Faserforshung and Textiltechnik 28 (4): 155-163 (1977) and in Faserforschung and Textiltechnik 27 (11): 561-570 (1976), and in West German Pat. Nos. 88,307, 92,136, and 93,100. A process for tanning a naturally grown microbial pellicle is described in U.S. Pat. No. 1,141,545. A method for coating synthetic fibers with microbial cellulose is described in U.S. Pat. No. 4,378,431 to Brown, Jr.
It has now been found that microbial polysaccharide pellicles, e.g., microbial cellulose pellicles, can be transformed from a naturally-occurring entangled fiber mass into laminar structures having enhanced physical properties by controlled physical manipulation of the pellicles.